The term "cytokines" encompasses a diverse group of soluble proteins that are released by one type of cell and mediate a biological effect on another cell type. Biological activities exhibited by cytokines include control of proliferation, growth, and differentiation of various cell types, among which are cells of the hematopoietic or immune systems.
Examples of cytokines include the interleukins (e.g., interleukins 1 through 10), the interferons (IFN.alpha., IFN.beta., and IFN.gamma.), tumor necrosis factor (TNF.alpha. and TNF.beta.), and colony stimulating factors. Examples of colony stimulating factors (CSF), which control growth and differentiation of hematopoietic cells, are granulocyte-CSF (G-CSF), granulocyte-macrophage-CSF (GM-CSF), macrophage-CSF (M-CSF or CSF-1), mast cell growth factor (MGF), and erythropoietin (EPO).
The biological activity of cytokines generally is mediated by binding of the cytokine to a receptor specific for that cytokine, located on the surface of target cells. Much research has been directed to identifying receptor(s) that bind a given cytokine (often referred to as the "ligand" for the receptor in question), and exploring the roles that endogenous ligands and receptors play in vivo.
Clinical utility has been demonstrated for a number of cytokines. Methods for enhancing the biological activity of cytokines administered in vivo would be beneficial in order to more fully realize the therapeutic potential of these proteins. Such enhancement of biological activity would allow reduction of the effective therapeutic dosages of cytokines to minimize side effects associated with administration of certain cytokines.